Hydraulic fluids

ABSTRACT

A hydraulic fluid suitable for use in a tube pressure filter, the hydraulic fluid comprising an aqueous solution of an inorganic salt and an organic material.

United States Patent Beazley et al. Oct. 2, 1973 1 HYDRAULIC FLUIDS1,822,449 9 1931 Nonamaker 252 74 2,455,117 11 1948 Glavis et al. 252/76x [75] Inventors: Kenneth Michael Beazley; Margaret 2,558930 6/195]Zisman e! a. 252/75 X CIlmPSO", both of COmwalL 2,665,312 1/1954 Ohlmannet al. 252/73 x England 2,898,294 8/l959 Priest et al 252 855 R i r2,552,775 5 1951 Fischer et al.. 252/8.5 c [73] AsMgnee' gush Clays jPoem 3,554,287 1 1971 Eilers 252/8.55 R x Company LimIted, Cornwall,gland OTHER PUBLICATIONS 22] Filed: Feb. 2, 1971 Appl. No.: 111,890

Foreign Application Priority Data Feb. 10, 1970 Great Britain 6,387/70References Cited UNlTED STATES PATENTS 3/1966 Gatzan 252/75 X Gregory,Uses and Applications of Chemicals and Related Materials, Reinhold Pub.Corp., New York, 1939,

Primary ExaminerLeon D. Rosdol Assistant ExaminerHarris A. PiitlickAttorney-Larson, Taylor & Hinds ABSTRACT 12 Claims, 1 Drawing FigureHYDRAULIC FLUIDS This invention relates to hydraulic fluids and moreparticularly is concerned with hydraulic fluids having a high specificgravity.

There exists a need for high-density hydraulic fluids in several typesof industry. For example, in tube pressure filters which are to be usedfor reducing the liquid content of wet, particulate solid materials inthe form of high density slurries it is important to use a hydraulicfluid of an appropriate density. Various kinds of tube pressure filtershave been described; see, for example, U.K. Pat. NO.907,485 and BelgianPat. No.7l7,264. Qne kind of tube pressure filter essentially comprisesa pair of generally coaxial tubular bodies forming between them anannular chamber; an impermeable elastic sleeve which is secured to theouter of the pair of tubular bodies and divides said chamber intogenerally coaxial and non-communicating inner and outer compartrnents,the inner compartment including an inlet, for a wet particulate solidmaterial to be pressure filtered, and a filter element which issupported by the inner of the pair of tubular bodies, the inner tubularbody and the filter element being constructed and ar ranged so as topermit liquid to flow through the filter element and the inner tubularbody while preventing the flow therethrough of the particulate solidmaterial, and the outer compartment including an inlet for a hydraulicfluid under pressure whereby the impermeable elastic sleeve can be urgedagainst a wet particulate solid material in the inner compartment tocompress the same and remove liquid therefrom; and means for displacingthe tubular bodies axially relative to one another to a position whereatthe particulate solid material can be discharged from the innercompartment. Hitherto, materials which could be used as high densityhydraulic fluids have possessed a numberof disadvantages, probably themost important of which has been their abrasive character.

It is an object of the present invention to provide a high densityhydraulic fluid which can be used in a tube pressure filter of the typehereinbefore described and which is non-abrasive in character.

Accordingly, the present invention provides a hydraulic fluidcomprising, in aqueous solution, one or more inorganic salts which havea density of at least 3 grams per cubic centimetre and a solubility ofat least 100 grams per litre in water at C, and a water-soluble organicmaterial which, on dissolution in water, produces a solution having aviscosity greater than that of water, such that the resulting solutionhas a specific gravity greater than 1.350, and a viscosity in the rangefrom 0.2 to 2.0 poise at C, and can withstand a pressure of at least 500p.s.i. without decomposing.

Preferably, a hydraulic fluid according to the present invention isnon-corrosive, non-toxic, non-flammable, and capable of withstanding apressure of 5000 p.s.i. without decomposing. It is also advantageous forthe hydraulic fluid to have a low freezing point and a low firsteutectic point.

The water-soluble organic material employed in the invention willgenerally be a water-soluble organic polymer, which may be in the formof a viscous liquid.

The most suitable inorganic salts are the bromides other alkali metals,and of the alkaline earth and transition-metals.

The watersoluble organic material can advantageously be a polyglycol,for example a polyethylene glycol, such as that manufactured under theregistered trade mark CARBOWAX" 600 0, or a polyethylene oxide.Alternatively a polyacrylate or a polyacrylamide can be used, in whichcase the pH of the hydraulic fluid should be 7 or slightly above. Themolecular weight of the polyglycol or polyethylene oxide is preferablyat least 5000 and that of the polyacrylate or polyacrylamide ispreferably at least 100,000.

Generally, the hydraulic fluid will comprise 5-50 parts by weight of awater-soluble organic material, for example polyethylene glycol, -200parts by weight of water, and 15-150 parts by weight of an inorganicsalt (calculated on an anhydrous basis). If an iodide is used in thehydraulic fluid, it is advantageous to add a small quantity of anaqueous thiosulphate solution, generally from 0.01 to 0.5 parts byweight of N/lO solution of so dium thiosulphate. If a relatively largequantity of the water-soluble organic material, e.g. a viscous organicliquid, is used, it is advantageous to incorporate an organic cosolvent,for example 5-20 parts by weight of acetone, since this can assist inthe dissolution of the water-soluble organic material and can act as alubricant.

For a better understanding of the invention, and to show how the samecan be carried into effect, reference will now be made, by way ofexample, to the accompanying drawing, which shows a diagrammatic partialcross-section of a tube pressure filter of the kind described in BelgianPat. No.717,264, and to the following Examples.

Referring to the drawing, the tube pressure filter 1 comprises an innertubular member In, an outer tubular member lb, sealing means 1c at eachend of the inner tubular member In, an impermeable elastic sleeve 1dsecured to the outer tubular member 1a to define with the tubularmembers inner and outer noncommunicating compartments 1e and If, aninlet 13 to the inner compartment 1e for slurry to be pressure filtered,a filter element 1g supported by the inner tubular member la, an inlet16 to the outer compartment lffor hydraulic fluid under pressure, and aninlet 21 for compressed air for use in discharging the filter cake. Inuse, it is preferable for the specific gravities of the hydraulic fluidand of the material being pressure filtered to be as nearly equal aspossible; the difference in specific and iodides of sodium andpotassium, but other useful 6 salts include the halides of other metals,for example the halides, generally the bromides and iodides, of thegravities is preferably not greater than 0.05. The invention will now beillustrated by the following Examples:

The polyethylene glycol had a molecular weight greater than 5,000. Theresulting solution was found to have a specific gravity of 1.450 undernormal temperature and pressure. Its viscosity at 20C. was within therange of from 0.2 2.0 poise. The hydraulic fluid was non-toxic,non-corrosive, and non-flammable. The hydraulic fluid was fed into thecompartment 1f of the tube pressure filter described above and anaqueous slurry of chalk whiting having a solids content of 49.5 percentby weight, which is equivalent to a specific gravity of 1.443, was fedinto the compartment 1e. The pressure of the hydraulic fluid was raisedto 1000 psig and maintained at this level for 2% minutes, during whichtime liquid was expressed from the slurry of chalk whiting and a filtercake was formed. The filter cake was then discharged and was found to be2 cm. thick and to weight 76 lb.(34 kg). The total cycle time was 3minutes, the water content of the filter cake was 18.5 percent by weightand the output rate was 1240 lb. per hour (562 Kg per hour). Aftercontinuous running for 7 days the apparatus was dismantled and examinedand there was found to be no wear of the metal parts which were incontact with the hydraulic fluid and no deterioration of the impermeableelastic sleeve 1d which formed the wall between the compartments of thetube pressure filter.

. EXAMPLE 2 A hydraulic fluid was prepared by mixing together thefollowing ingredients (all in parts by weight) until a homogeneoussolution resulted:

Potassium iodide 100 Polyethylene glycol 29 Acetone 8 N/l Sodiumthiosulphate solution 0.2

Water 88 The polyethylene glycol had a molecular weight greater than5,000. The resulting solution was found to have a specific gravity of1.510 under normal temperature and pressure and had a viscosity of 0.40poise at 20C. It was non-toxic, non-corrosive, non-flammable andwithstood a compression of 500 p.s.i. without decomposition.

EXAMPLE 3 A hydraulic fluid was prepared by mixing together thefollowing ingredients (all in parts by weight) under a homogeneoussolution resulted:

Sodium bromide 100 CARBOWAX 6000 19 Water 126 This solution was found tohave a specific gravity of 1.470 under normal temperature and pressureand had a viscosity of 0.38 poise at 20C. It was non-toxic,noncorrosive, non-flammable and withstood a pressure of 500 p.s.i.without decomposition.

The hydraulic fluids described in Examples 2 and 3 above have beensuccessfully employed in a tube pressure filter of the type hereinbeforedescribed.

We claim:

1. A hydraulic fluid consisting essentially of an aqueous solutioncontaining from 50 to 200 parts by weight of water, from 15 to 150 partsby weight, of at least one inorganic halide which has a density of atleast 3 grams per cubic centimeter and a solubility of at least gramsper litre in water at 0C, and from 5 to 50 parts by weight of awater-soluble organic material which is selected from the groupconsisting of polyglycols and polyethylene oxides having a molecularweight of at least 5,000 and of salts of polyacrylic acids andpolyacrylamides having a molecular weight of at least 100,000 and whichorganic material, on dissolution in water, produces a solution having aviscosity higher than that of water, wherein the aqueous solution has aspecific gravity greater than 1.350, a viscosity in the range from 0.2to 2.0 poise at 20C, and can withstand a pressure of at least 500 p.s.i.without decomposing.

2. A hydraulic fluid as claimed in claim 1 in which the inorganic halideis an iodide and in which the hydraulic fluid contains from 0.01 to 0.5parts by weight of an N/10 aqueous solution of sodium thiosulphate.

3. A hydraulic fluid as claimed in claim 1 in which the hydraulic fluidcontains from 5 to 20 parts by weight of acetone to assist thedissolution of said water-soluble material.

4. A hydraulic fluid as claimed in claim 1, in which the inorganichalide is a halide of an alkali metal.

5. A hydraulic fluid as claimed in claim 1 in which the inorganic halideis a halide of an alkaline earth metal.

6. A hydraulic fluid as claimed in claim 1 in which the inorganic halideis a halide of a transition metal.

7. A hydraulic fluid as claimed in claim 4 in which the alkali metal issodium.

8. A hydraulic fluid as claimed in claim 4 in which the alkali metal ispotassium.

9. A hydraulic fluid as claimed in claim I in which the inorganic halideis a bromide.

10. A hydraulic fluid as claimed in claim 1 in which the inorganichalide is an iodide.

11. A hydraulic fluid as claimed in claim 1 in which said water-solubleorganic material comprises a polyethylene glycol.

12. A hydraulic fluid as claimed in claim 1, in which said water-solubleorganic material is a salt of a polyacrylic acid and in which the pH ofthe aqueous solution is at least 7.

2. A hydraulic fluid as claimed in claim 1 in which the inorganic halideis an iodide and in which the hydraulic fluid contains from 0.01 to 0.5parts by weight of an N/10 aqueous solution of sodium thiosulphate.
 3. Ahydraulic fluid as claimed in claim 1 in which the hydraulic fluidcontains from 5 to 20 parts by weight of acetone to assist thedissolution of said water-soluble material.
 4. A hydraulic fluid asclaimed in claim 1, in which the inorganic halide is a halide of analkali metal.
 5. A hydraulic fluid as claimed in claim 1 in which theinorganic halide is a halide of an alkaline earth metal.
 6. A hydraulicfluid as claimed in claim 1 in which the inorganic halide is a halide ofa transition metal.
 7. A hydraulic fluid as claimed in claim 4 in whichthe alkali metal is sodium.
 8. A hydraulic fluid as claimed in claim 4in which the alkali metal is potassium.
 9. A hydraulic fluid as claimedin claim 1 in which the inorganic halide is a bromide.
 10. A hydraulicfluid as claimed in claim 1 in which the inorganic halide is an iodide.11. A hydraulic fluid as claimed in claim 1 in which said water-solubleorganic material comprises a polyethylene glycol.
 12. A hydraulic fluidas claimed in claim 1, in which said water-soluble organic material is asalt of a polyacrylic acid and in which the pH of the aqueous solutionis at least 7.